Poly(biphenyl ether sulfone)s form a specific class of poly(aryl ether sulfone)s. These amorphous technopolymers are materials of choice notably for the ultimate in toughness with rather good chemical resistance, superior to most of commercially available transparent resins but lower than that of ultra-performance polymers like poly(aryl ether ketone)s.
Precisely, poly(aryl ether ketone)s offer an exceptional balance of technical properties, namely high melting point, excellent thermal stability, high stiffness and strength, good toughness and really excellent chemical resistance, including excellent resistance to environmental stress rupture resistance. However, the somewhat low glass transition of these materials limits theirs use in certain specific applications where the use temperature is above 170° C.: this is primarily because of the loss of modulus as the glass transition is traversed.
In lots of applications, the exceptional balance of technical properties offered by poly(aryl ether ketone)s is plainly appreciated and in said applications, there is e.g. no need for a material that would have improved load bearing capabilities above the Tg of neat poly(aryl ether ketone). An important problem remains still, due to the high cost of the poly(aryl ether ketone)s, which prevents the skilled person from using said poly(aryl ether ketone)s as widely as technically desirable for the encompassed applications, in particular when the shaped articles or at least some part(s) thereof are contacted, temporarily or permanently, with an aggressive chemical environment, and, more particularly when the shaped articles or at least one or more parts thereof are in addition submitted, temporarily or permanently, to stress.
There remains thus a strong need for a polymer composition with a lower cost than that of poly(aryl ether ketone) compositions, but a chemical resistance at least substantially the same as the one obtained by said poly(aryl ether ketone) compositions.
The challenge appeared tricky for the Applicant, especially in view of the teachings of U.S. Pat. No. 4,804,724, as commented below.
U.S. Pat. No. 4,804,724, the whole content of which is herein incorporated by reference, describes blends comprising a poly(biphenyl ether sulfone) and a poly(aryl ether ketone). Per U.S. '724, these blends, at intermediate compositions (such as 50 parts of PPSU and 50 parts of PEEK), exhibit an “interesting” balance of properties, in particular an intermediate toughness and modulus (thus intermediate load bearing capabilities) in the range between the (low) poly(aryl ether ketone) Tg and the (high) poly(biphenyl ether sulfone) Tg, and an intermediate chemical resistance (including an intermediate environmental stress rupture resistance) in certain chemical environments (ethyl acetate, 1,1,1-trichloroethane, toluene and acetone) in the range between the (high) chemical resistance of the poly(aryl ether ketone) and the (substantially lower) chemical resistance of the poly(biphenyl ether sulfone). Thus, the teachings of U.S. '724 are twofold: (1) poly(biphenyl ether sulfone)s can be used for increasing the load bearing capabilities above the Tg of neat poly(aryl ether ketone)s, and (2) adding a poly(biphenyl ether sulfone) to a poly(aryl ether ketone) is expected to cause a substantial decrease of the chemical resistance.
Thus, in short, the skilled in the art, in view of the teachings of U.S. '724, would have understood that replacing part of the poly(aryl ether ketone) contained in a poly(aryl ether ketone) composition by a usually more cost-attractive polymer, in particular a poly(biphenyl ether sulfone), should not be an appropriate means to solve the complex problem of reducing the cost of the poly(aryl ether ketone) composition while substantially maintaining the chemical resistance conferred by the poly(aryl ether ketone).